1. Field of the Invention
The present invention relates to a microscopic geometry cutting device and microscopic geometry cutting method for providing a microscopic asperity on a surface of a workpiece.
2. Description of Related Art
Conventionally, a microscopic surface cutting device and microscopic cutting method disclosed in document (JP-A-2006-123085) have been known as a device and method for providing a microscopic asperity on a surface of a workpiece. The microscopic surface cutting device includes: a first reciprocating slide mechanism; a second slide mechanism that moves for intermittent positioning in a direction orthogonal to a moving direction of the first slide mechanism; a tool moving mechanism that quickly and finely controls cutting depth of a cutter in a direction orthogonal to moving directions of the first and second slide mechanisms; and a position detector that generates a pulse signal in accordance with a movement of the first slide mechanism. For providing a microscopic surface geometry on the surface of the workpiece, the cutting depth of the cutter is quickly changed by the tool moving mechanism in synchronism with the pulse signal generated from the position detector during a movement of the first slide mechanism in a positive direction, and the cutter is moved away from the workpiece during a movement of the first slide mechanism in a reverse direction. Further, the second slide mechanism is feed in increments with each reciprocation of the first slide mechanism. In this manner, the microscopic surface geometry is provided on the surface of the workpiece. In the device and method as disclosed in the above-described document, during the movement of the first slide mechanism in the positive direction, position information of the first slide mechanism is detected by the position detector and the pulse signal from the position detector is counted. Subsequently, whether or not a counted value is coincident with a predetermined value is determined, a trigger signal is output when the count value is coincident with the predetermined value, and then the cutting depth of the cutter is quickly changed by the tool moving mechanism by the trigger signal. In such arrangement, it is necessary to count the pulse signal generated from the position detector and determine whether the counted value is coincident with the predetermined value. Accordingly, a timing for advancement and retraction of the cutter is likely to be delayed and a highly accurate microscopic surface geometry may not he provided on the surface of the workpiece. Especially, when machining a roller for microlens transcription molding or a transcription molding die used for transcription molding of a plurality of microlenses on a sheet, a microlens molding section to be machined molds a circular minute unit lens (e.g. concave or convex lens) of which outer diameter is about 10-300 μm and depth is 0.6-50 μm. Accordingly, the highly accurate microscopic surface geometry cannot be provided on the surface of the workpiece when the timing for the advancement and retraction of the cutter fluctuates. Additionally, in the device and method as disclosed in the above-described document, a machining condition is determined generally by selecting a feed speed through a trial-and-error process while considering a necessary time or the like for machining a target geometry. However, the above-described method requires considerable time to determine the machining condition. Further, due to a dynamic characteristics to quickly change the cutting depth of the cutter by the tool moving mechanism, amplitude of an actual movement track of the cutter is reduced or phase-delay is generated relative to a target track of the cutter as shown in FIG. 11. Furthermore, resonance is occasionally generated due to an intrinsic frequency of a device having a slide mechanism. Thus, the movement track and target track of the cutter are not coincident, whereby a cutting error is increased.